In the past, vibrating screen machines are normally made of a box-like structure mounted on flexible springs and contain one or multiple layers of screen mesh to sort granular materials. The different sized openings in the mesh allow sizing of materials according to the size of these openings. The box structure usually contains an eccentric weighted shaft that shakes the box and its screen mesh to agitate and separate the granular materials fed into the top of the machine.
Vibrating screens can be categorized in many ways. Horizontal (see FIG. 1) and sloped screens (see FIG. 2) are common ways to categorize these screens.
The two designs are used in different applications. The sloped screen decks are desirable in applications where there is a high percentage of “oversize” material that is larger than the openings in the screen cloth. The opening size is determined by the size of the material desired to be removed from the feed material. When too much material is riding on the deck, the material is too deep to efficiently allow fine material to sift through the bed of material and get to the screen cloth for separation. The horizontal screens are more effective when there are difficult conditions requiring more retention time on the screen decks; for example, a high amount of “near size” material. Also, applying water to clean the material is more desirable on horizontal decks, since the sloped decks will wash material down and off the end before it can drop through the screen cloth.
There are many types of triple shaft screens. One could gather a group of prior art sloped screens, each of which has a different single set angle at which the decks are sloped. One thing in common with these sloped machines is that they still utilize a horizontal constructed gear case (See FIG. 2).
Typically, the three-shaft vibrating mechanism consists of three eccentrically weighted shafts geared together, so that the center or second shaft rotates counter of the adjacent first and third shafts. This mechanism utilizes a common gear case with common oil splash lubrication for all gears and bearings. All three shafts are geared together on a common horizontal plane to maintain uniform splash lubrication on all three shaft/bearing assemblies.
The counter rotating center eccentric adds or subtracts from the total vibrator thrust, depending on phase with the outer two eccentrics to create the unique oval motion on the vibrating screen box. It is well known that an oval stroke is preferred and that the manner for producing an oval stroke is also well known.
It is well known that a sloped gear case will, at least when the screen is not operating, let lubrication oil pool to the low end, thus increasing the oil depth on the low end. It is also widely believed that since the oil flows to the lower end, there is a danger of starving the bearings toward the high end of oil. It is also believed that simply increasing the amount of oil in the gear case, and thereby increasing the overall oil depth, would create more splash in the upper end, but would flood the lower bearings, causing excessive heat.
It is also widely believed that if a user desires the ability to utilize triple shaft screening over a wide range of angles, that a collection of several sloped screens, each with a single fixed slope angle, be available. However, this can be extremely expensive and difficult to exchange on the machine in which the screen is operating.
Requiring a horizontal mounting plane of the shaft housings for the multiple shaft style screen which is operating on a sloped orientation requires greater distance between the decks directly above and below the shaft housings since all the housings are not aligned along the upper deck.
Consequently, there is a need for a relatively inexpensive way to provide a triple shaft screen to operate over a wide range of screen slope angles and not require different screens built on different slopes for different applications.